Signal processing methods implemented in practical communications systems are typically designed under the assumption that underlying noise and interference statistics are Gaussian. Although this assumption finds strong theoretical justification in the Central Limit Theorem, the noise and interference processes commonly present in modem mobile communications systems are often not Gaussian, but more impulsive in nature. Examples of such impulsive noise and interference include motor vehicle ignition noise, switching noise from electromechanical equipment, lightening, and heavy bursty interference. Current signal processing systems are typically not optimally designed for channels having this type of noise and interference, because the implemented signal processing techniques assume the noise statistics are Gaussian.
Many techniques developed to cope with impulsive noise are ad hoc, largely based on signal clipping and preprocessing prior to the application of Gaussian based techniques. Clipping involves quantizing the amplitude values of the input signal. Clipping replaces the amplitude value of an input signal, which is above or below a threshold value, or values, with a respective constant value. The constant value(s) are processed in lieu of the actual amplitude value(s) of the input signal. The input signal, with clipped values, is typically processed under the assumption that the statistics of the noise are Gaussian. A disadvantage of clipping is that it introduces significant distortion to the input signal, thus adversely affecting the processing performance of the communication system.
Clipping the amplitude of the input signal is only effective if the amplitude of the input signal is above or below the specific threshold values. These threshold values are typically determined by the limits of the hardware used in a receiver of a communications system. That is, the threshold values are often determined to take advantage of the full dynamic range of the analog to digital (A/D) converter(s) of the receiver. Thus, if impulsive noise, added to the input signal, does not cause the amplitude of the signal to exceed a specific threshold, clipping will not be implemented. This adversely affects processing performance, because the input signal being processed is contaminated with impulsive noise.
A need exists therefore, for a system and method of processing signals to alleviate impulsive noise distortion without suffering the above described disadvantages.